Persistent obstructive airways disease is common among WTC-exposed firefighters, though rare in this population before 9/11/2011. There is preliminary evidence that bronchial hyperreactivity is associated with excessive immediate (pre-post 9/11) pulmonary function decline rates, but it remains unclear if that was cause or effect. This proposal is for a re- examination, ten years later, of bronchial reactivity and lung function for a large group firefighters who had lung function and bronchial reactivity tests in the early post-9/11 period. Specific aims are (1) to quantify the change in bronchial reactivity over 10 years; (2) to determine whether initial and/or subsequent bronchial reactivity is associated with the decline in lung function from 2002 to 2013; and (3) to determine whether anti-inflammatory treatment (mainly inhaled corticosteroids [ICS]) ameliorates bronchial hyperreactivity and/or lung function decline. Approximately 350 WTC-exposed firefighters will have detailed reviews of medical records, and face-to-face interviews, reviewing medical and firefighting histories, with special attention to the use of inhaled steroids. Detailed pulmonary function tests will also be conducted, including measurements of bronchial reactivity. Statistical analysis will be both categorical, comparing average lung function decline rates in subgroups with or without OAD and with high or normal bronchial reactivity, and by multivariate analysis. The results should define the natural history of WTC-associated OAD, determine whether clinical outcomes varied according to bronchial reactivity, assess the influence of anti- inflammatory treatment on outcomes.